As an example of an automatic transmission apparatus suitable for a front-engine rear-drive vehicle, a dual clutch transmission apparatus is disclosed in JP2003-148602A (Reference 1). In this specification, the dual clutch transmission apparatus having a dual clutch mechanism, i.e., having an automatic clutch mechanism including two frictional clutches that are engaged or disengaged alternately, is disclosed.
In this dual clutch transmission apparatus, torque is firstly transmitted to a first input shaft via a first frictional clutch of the dual clutch mechanism from a drive shaft such as an output shaft of an engine, and then torque is transmitted to a second input shaft formed in a hollow shape. The second input shaft is coaxially arranged with the first input shaft on its peripheral portion. When a vehicle is driven in a normal condition, the first and the second frictional clutches of the dual clutch mechanism are controlled by a control device of the dual clutch transmission apparatus in a manner that; 1) during a shift operation, the first and the second frictional clutches are in a partial clutch engagement state, which results in one torque (corresponding to, for example the first frictional clutch) being increased and the other torque (corresponding to the second frictional clutch) being decreased at the same time, and vice versa, and 2) after the shift operation has ended, the first frictional clutches are in a completely engaged state, which results in the torque reaching a maximum value while the second frictional clutches are being disengaged and the other torque corresponds to the second frictional clutch falling down to 0 value, and vice versa. This dual clutch transmission apparatus includes a counter shaft arranged in parallel with the first and second input shafts. Multiple gear trains are arranged between the second input shaft and the counter shaft. The multiple gear trains are actuated to establish a 1st shift stage, a 3rd shift stage and a 5th shift stage, respectively. Arranged between the first input shaft and the counter shaft are multiple gear trains that are actuated to establish a 2nd shift stage, a 4th shift stage, a reverse shift stage and a low-speed shift stage for emergency. Housed in the transmission are also four switching clutches, which are used to change shift stages. The counter shaft is connected to an output shat, which extends coaxially with the first input shaft in a rearward direction of the transmission, via a final transition gear train.
The control device of this dual clutch transmission apparatus controls the first frictional clutch and the second frictional clutch to be engaged or disengaged in turns, and further the control device selects each shift stage, depending on a condition of a vehicle, such as an accelerator opening degree, and a speed of the engine, a speed of the vehicle, or the like. For example, when the condition of the vehicle matches a driving of a vehicle at the 2nd shift stage, the control device selects the 2nd shift stage and the first frictional clutch so that a driving of a vehicle at the 2nd shift stage is achieved. When the condition of the vehicle matches a driving of a vehicle at the 3rd shift stage, for example, because of an accelerator opening degree increasing, the control device selects the 3rd shift stage and the second frictional clutch so that the driving of the vehicle at the 2nd shift stage is changed to a driving of the vehicle at the 3rd shift stage. Likewise, the control device selects either the first frictional clutch or the second frictional clutch in turns as well as selecting a gear train appropriate to a condition of the vehicle, wherein the vehicle drives at a shift stage appropriate to a condition of the vehicle. When a speed of the vehicle declines while the vehicle is in motion at the 1st shift stage, the control device selects the gear train for the low-speed shift stage for emergency and the first frictional clutch so that a driving mode of the vehicle is changed to a low-speed driving mode for emergency. The above-mentioned operation is achieved when a shift lever is set to be at a forward movement position. However, when the shift lever is set to be at a reverse movement position under the condition that the vehicle is temporarily stopped, the control device selects the gear train for the reverse shift stage and the first frictional clutch so that the vehicle can reverse.
In the dual clutch transmission apparatus disclosed in Reference 1 being suitable for the front-engine rear-drive type vehicle, the first input shaft is arranged coaxially with the output shaft. On the other hand, a dual clutch transmission apparatus applicable for a use in a front-engine front-drive type vehicle is disclosed in JP2006-002789 (Reference 2, paragraphs 3-9, FIG. 8). The dual clutch transmission apparatus (Reference 2) differs from the aforementioned apparatus (Reference 1) in which, in the dual clutch transmission (Reference 2), a first intermediate shaft and a second intermediate shaft are arranged in parallel with first and second input shafts. Mounted between the first input shaft and the first and second intermediate shafts is a first gear change mechanism having plural gear trains for the 1st shift stage, the 3rd shift stage, the 5th shift stage and the 7th shift stage. Mounted between the second input shaft and the first and second intermediate shafts is a second gear change mechanism having plural gear trains for the 2nd shift stage, the 4th shift stage and the 6th shift stage. Mounted between the first input shaft and the second intermediate shaft is a gear train for the reverse shift stage.
According to the dual clutch transmission apparatus disclosed in Reference 1, the eight gear trains for the 1st shift stage, the 2nd shift stage, the 3rd shift stage, the 4th shift stage, the 5th shift stage, the low-speed shift stage for emergency, the reverse shift stage and the final transmitting gear train are mounted between the two input shafts, the output shaft and the counter shaft, and further, the four switching clutches are provided at the apparatus. These components are all arranged in series along the axis. As a result, the axial length of the gearbox becomes larger, and the number of gears is increased with respect to the number of shift stages. Meanwhile, in the apparatus disclosed in Reference 2, mounted on the two input shafts, the single output shaft and the two intermediate shafts, arranged in parallel therewith, are nine gear trains for the 1st shift stage, the 2nd shift stage, the 3rd shift stage, the 4th shift stage, the 5th shift stage, the 6th shift stage, the 7th shift stage, the reverse shift stage and the final transmitting gear train, and the four switching clutches. The components, which are partially arranged in parallel, are all arranged along the axis in series. As a result, although the axial length of the gearbox is shortened, it may be difficult to adapt the apparatus disclosed in Reference 2 to the front-engine rear-drive type vehicle as it is. Additionally, gears, whose diameter differs largely from each other within each gear train, need to be provided at dual clutch transmission apparatuses disclosed in JP2003-148602A and in JP2006-002789 so that a range of changes in gear ratio, which is obtained by the number of rotations of the driven-wheel-side shaft being divided by the number of rotations of the engine-side shaft, may be widely and freely selected. However, there are limits on diameter of gears to be minimized. Therefore, the transmission apparatus may become larger.
A need thus exists to provide a dual clutch transmission apparatus applicable for a use in a front-engine rear-drive type vehicle, and the dual clutch transmission apparatus with which a range of changes in gear ratio may be widely and freely selected and further, with the dual clutch transmission apparatus, the size of the transmission apparatus being arranged to become smaller by changing a configuration of each gears of the apparatus.